The objectives of the proposed research is to study intestinal microsomal p-nitrophenolUDPglucuronyl transferase (UDPGT) in order to eventually relate the enzyme activity measured in vitro to that which occurs in vivo. Detergent-solubilized enzyme will be purified from intestinal microsomes. The activity of the pure enzyme will be determined in a carefully defined system in which whole microsomal activity can also be measured. In this manner microsomal activity can be accurately quantitated such that the effect of various parameters, such as prior exposure to xenobiotics, can be determined. In addition, the contribution of other enzymes to p-nitrophenol conjugation will be determined as well as the ability of the pure enzyme to conjugate other xenobiotics.